Gas-discharge overvoltage arrester

ABSTRACT

A voltage overload arrester comprising a pair of shaped electrodes having surface portions in spaced adjacent relation to each other and gas impermeably sealed within an insulating housing. The adjacent surface portions of each electrode are provided with a thin coating of an alloy of a material having a high electron emission ability, such as Ba, and a material having a stabilizing effect on the electron work function of such emission material, such as Al. The method comprises forming the alloy-coated electrodes and subjecting them to heat of about 700* to 900* C. so as to eliminate all impurities from the alloy coating.

United States Patent Bahr et a1.

[54] GAS-DISCHARGE OVERVOLTAGE ARRESTER [72] Inventors: Alex Bahr; Gerhard Peche, both of Berlin,

Germany Siemens Alitlengesellschalt, Berlin and Munich, Germany [22] Filed: Sept. 24, 1970 [21] Appl.No.: 75,140

[73] Assignee:

301 Foreign Application Priority om Oct. 3, 1969 Germany ..P 19 50 090.4

52 us. Cl ..317/61, 313/218, 317/70 [51] Int. Cl. ..H02h 9/06 [58] FieldofSearch ..3l7/70,61;3l3/2l8;315/36 [56] References Cited UNITED STATES PATENTS 2,141,655 12/1938 Kott ..313/218X July 11, 1972 3,286,119 ll/l966 Sugawaraetal.....

..313/218 X 3,530,327 9/1970 Zollweg et al. ...313/2l8 X 3,535,582 10/1970 Kawiecki ..317/70X.

Primary Examiner-James D. Trammell Anomey-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT A voltage overload arrester comprising a pair of shaped electrodes having surface portions in spaced adjacent relation to each other and gas impermeably sealed within an insulating housing. The adjacent surface portions of each electrode are provided with a thin coating of an alloy of a material having a high electron emission ability, such as Ba, and a material having a stabilizing effect on the electron work function of such emission material, such as Al. The method comprises forming the alloy-coated electrodes and subjecting them to heat of about 700 to 900 C. so as to eliminate all impurities from the alloy coating.

10 Clalns, 1 Drawing Figure GAS-DISCHARGE OVERVOLTAGE ARRESTER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a voltage overload protection device, and more particularly to a voltage overload arrester having electron-emission materials therein and a method of producing the same.

2. Prior Art German Pat. No. 615,506 teaches a voltage overload arrester device wherein the work surfaces of the electrodes are positioned adjacent to each other within the device and are provided with an additional layer of a material. This material apparently functions to lower the work function of the electrodes and allows the electrodes to function as a cathode, i.e. an electron-emission device. Such electron-emission device in an over-load arrester functions to lower the voltage drop and the power loss during periods of a given overloading current.

The capacitance, of a voltage overloadarrester essentially depends on theglowing or arc-burning voltage, the arcpassing current and on the cross sectional dimension of the electrode surfaces, as well as the power supply lines. Of course, the cross sectional dimension is limited by the actual size of a particular overload arrester. However, an increase in the field electron emission at such electrode surfaces, which function as a cathode (sometimes referred to herein as a cold arc-cathode) would materially increase the capacitance of an overload arrester.

Prior art teaches that a decrease of the electron work function in a glow discharge tube or the like by activation of a cold arc cathode is achieved with an additional layer containing barium or another earth alkali metal. However, such earth alkali metal activated electrode layers have a serious disadvantage in that their work function changes after an impactcurrent stress. Apparently, the change in the electron work function of such materials occur because of the presence of impurity. Such impurities fail to volatilize or decay during heat treatment operations, which are necessarily limited by the physical characteristics of thematerials per se. During an impact-current stress irreversible changes in the electrode work function take place at the cold arc cathode and materially infiuence ignition potential of the voltage overload arrester.

SUMMARY OF THE INVENTION The invention provides a means of avoiding adverse changes in electron work functions of cold arc cathodes in a voltage overload arrester. In accordance with the principle of the invention, the electron workfunction of an activated cold arc cathode is stabilized by the incorporation of a material having a stabilizing effect on the electron work function of the activated surface so that such work function and the ignition potential remain essentially unchanged after an impact-current stress, particularly as compared with prior art activated cold arc cathodes. This stabilizing material is combined with an electron emission material to form an alloy-like mixture and coated as a thin layer on the work surface of the electrode and subjected to heat of about 700 to 900 C. to drive off impurities and positioned for operation in a voltage overload arrester. Preferably, the stabilizing material is aluminum and the electron emission material is barium, although other suitable materials can also be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing illustrates an elevated diagrammatic cross sectional view, of an exemplary embodiment of a voltage overload arrester constructed in accordance with principle of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the principles of the invention, suitable electrodes are formed of, for example, a Ni-Fe alloy or a Nifurther material at the work surfaces thereof. These work surfaces, in assembly, form spaced apart adjacent surfaces of an assembled voltage overload arreSterQThe coating material on the outer periphery of such work surfaces contains a substantially uniform intermixture of a first material having a relatively high electron emission ability and a second material having a stabilizing effect on the electron work function of such first material.

Preferably, the first material having a relatively high electron emission is barium and the second materialhaving a stabilizing effect on the electron work function of such first material is aluminum. The material having a relatively high electron emission ability can also be selected from rare earth metals per se or in combination with earth alkali metals, such as barium. The material having stabilizing effect on the elec-.

tron work function of such electron-emission material can be selected from relatively low melting metals that readily combine with or alloy with such electron emission materials. Such 'low melting metals can be utilized per se or in combination with aluminum. These various electron-emission materials and electron work function stabilizing materials are combined so as to form a mixture wherein all the components thereof are interconnected as in an alloy.

A voltage overload arrester constructed in accordance with the principle of the invention utilizing aluminum as the electron work function stabilizing material is particularly advantageous. Thus, a voltage overload arrester having aluminum as a component of the coating on its electron work surfaces exhibits a stabilized electrode work function and a stabilized work function per se. Further, the ignition potential of such an aluminum containing voltage overload arrester undergoes significantly lower fluctuation after an impact-current stress compared with known voltage overload arresters having electrodes provided with activated layers of earth alkali metals,

More particularly, a voltage overload arrester of the invention has a significant or essentially lower electron work function fluctuations of the cold arc cathodes thereof after an impact-current stress. Particularly, the cold arc cathode (i.e. the

electrode layer or coating containing a material having a relatively high electron emission ability) is composed of barium and aluminum. Generally, the coating is a uniform intermixture or alloy of barium, which is present in amounts ranging from about 30 percent to about 90 percent by weight and of aluminum, which is present in amounts ranging from about l0 percent to about 70 percent by weight. Extremely stable function behavior is achieved by providing an alloy of about 50 percent by weight barium and about 50 percent by weight aluminum.

A method of producing a voltage overload arrester of the invention generally comprises forming an alloy of a first material having a relatively high electron emission ability, i.e. Ba, and second material having a stabilizing effect on the electron work function of the first material, i.e. Al. This alloy, preferably Ba-Al, is then applied as a relatively thin layer on the outer periphery of the electrode work surfaces. The alloycoated electrodes are then subjected to heat substantially in the range of about 700 to about 900 C. in an inert atmosphere for a period of time sufficient to eliminate or drive off all impurities from the alloy coating. The heat treated electrodes are then combined with the housing structure of a configured arrester and placed in condition for operation. Alternatively, the alloy-coated electrodes can first be combined with the housing structure of a configured arrester and subjected to the aforesaid heat treatment. After cooling, the interior of the arrester housing can be evacuated or filled with an inert gas as desired and the arrester placed in condition for operation.

Referring now to the exemplary embodiment illustrated in the drawing, a voltage overload arrester 10 is provided with a somewhat tubularly-shaped insulating body 1. A pair of generally frustum-shaped electrodes 2 and 3 are positioned FeCo alloy and provided with a relatively thin coating of a within the body 1 and sealed therein by a gas impervious seal means (not shown). The electrodes 2 and 3 are positioned so that their respective work or frontal surfaces 2a and 3a, respectively, are positioned to face each other in a spaced adjacent relation.

7 Preferably, the insulating body or housing structure 1 is composed of glass or a ceramic material. The electrodes are preferably composed of a nickel-iron or a nickel-iron-cobalt alloy.

It will be noted that the electrodes 2 and 3 have end portions protruding beyond the confines of the insulating housing structure 1 so as to define contact terminals for connecting with a particular electrical circuit wherein the safety of the voltage overload arresters is desired. As indicated before, the arrester is formed to be gas impermeable so that the interior thereof may be substantially completely evacuated or filled in an inert or noble gas as desired.

A relatively thin layer 4 is provided on the outer periphery of the adjacent work surfaces 2a and 3a respectively. The layer 4 is composed of an alloy of a first material having a relatively high electron-emission ability and a second material having a stabilizing effect on the electron work function of such first material. Preferably, the layer 4 is composed of a Ba- Al alloy containing about 50 percent by weight barium and about 50 percent by weight aluminum. Of course, only one of the surfaces 2a or 3a need to be provided with the coating in order to achieve a functional overload arrester but preferably both of these surfaces 2a and 3a are provided with such a coatmg.

After assembly, the voltage overload arrester 10 is submitted to a heat treatment having temperatures inthe range of about 700 to about 900 C. for a period of time sufficient to eliminate all of the impurities from the Ba-Al alloy.

Various modifications or changes may be effected to the exemplary embodiment described herein without departing from the spirit and scope of the novel concepts of the invention.

We claim as our invention:

1. A gas-discharge voltage overload arrester comprising, a gas impermeable housing having an interior chamber, a pair of shaped electrode members positioned in workingrelationship within said interior chamber, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer on at least one of said work surfaces, said layer consisting essentially of a substantially uniform intermixture of a first material having a relatively high electron emission ability and at least aluminum.

2. A gas-discharge voltage overload arrester as defined in claim 1 wherein the first material in the layer is Ba outer peripheral.

3. A gas-discharge voltage overload arrester as defined in claim 1 wherein the outer peripheral layer is composed of about 30 percent to 90 percent by weight of Ba and about 10 lO jacently spaced from one another and having work surfaces in spaced facing relation to each other, a means sealing said electrodes to said housing to form a gas-impermeable housing, said electrodes protruding beyond said means to form contact points, and an outer peripheral layer on each of said surfaces, said layer consisting essentially of an alloy of a material having a relatively high electron emission ability and at least alummum.

6. A gas-discharge voltage overload arrester as defined in claim 5 wherein the aluminum is present in the outer peripheral layer in amounts ranging from about 10 percent to about 70 percent by wei ht.

7. A gas-discharge vo tage overload arrester comprising a gas impermeable housing having an interior chamber, a pair of shaped electrode members positioned in working relation within said interior chamber, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer on each of said work surfaces, said layer consisting essentially of a substantially uniform intermixture of about 30 percent to about percent by weight Ba and about 10 percent to about 70 percent by weight Al.

8. A gas-discharge voltage overload arrester as defined in claim 7 wherein the outer peripheral layer is composed as a uniform intermixture of about 50 percent by weight Ba and about 50 percent by weight Al.

9. A method of producing a gas-discharge voltage overload arrester comprising: coating a relatively thin layer of a substantially uniform inter-mixture of a first material having a relatively high electron-emission ability and at least aluminum onto a work surface of an electrode, subjecting the coated electrode to a heat treatment including temperatures in the range of about 700 to 900 C. for a period of time sufficient to eliminate any impurities within said layer, and assembling such heat treated electrodes into a gas impermeable voltage overload arrester structure so that said electrode work surfaces are spaced in facing adjacent relation from each other.

10. A method as defined in claim 9 wherein the first material is Ba and is present in amounts ranging from about 30 percent to about 90 percent by weight and the second material is Al and is present in amounts ranging from about 10 percent to about 70 percent by weight. 

1. A gas-discharge voltage overload arrester comprising, a gas impermeable housing having an interior chamber, a pair of shaped electrode members positioned in working relationship within said interior chamber, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer on at least one of said work surfaces, said layer consisting essentially of a substantially uniform intermixture of a first material having a relatively high electron emission ability and at least aluminum.
 2. A gas-discharge voltAge overload arrester as defined in claim 1 wherein the first material in the layer is Ba outer peripheral.
 3. A gas-discharge voltage overload arrester as defined in claim 1 wherein the outer peripheral layer is composed of about 30 percent to 90 percent by weight of Ba and about 10 percent to 70 percent by weight of Al.
 4. A gas-discharge voltage overload arrester as defined in claim 1 wherein the outer peripheral layer is composed of about 50 percent by weight of Ba and about 50 percent by weight of Al.
 5. A gas-discharge voltage overload arrester comprising, a housing composed of an insulating material having a pair of openings formed therein, a pair of shaped electrodes extending through the openings of said housing and positioned adjacently spaced from one another and having work surfaces in spaced facing relation to each other, a means sealing said electrodes to said housing to form a gas-impermeable housing, said electrodes protruding beyond said means to form contact points, and an outer peripheral layer on each of said surfaces, said layer consisting essentially of an alloy of a material having a relatively high electron emission ability and at least aluminum.
 6. A gas-discharge voltage overload arrester as defined in claim 5 wherein the aluminum is present in the outer peripheral layer in amounts ranging from about 10 percent to about 70 percent by weight.
 7. A gas-discharge voltage overload arrester comprising a gas impermeable housing having an interior chamber, a pair of shaped electrode members positioned in working relation within said interior chamber, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer on each of said work surfaces, said layer consisting essentially of a substantially uniform intermixture of about 30 percent to about 90 percent by weight Ba and about 10 percent to about 70 percent by weight Al.
 8. A gas-discharge voltage overload arrester as defined in claim 7 wherein the outer peripheral layer is composed as a uniform intermixture of about 50 percent by weight Ba and about 50 percent by weight Al.
 9. A method of producing a gas-discharge voltage overload arrester comprising: coating a relatively thin layer of a substantially uniform inter-mixture of a first material having a relatively high electron-emission ability and at least aluminum onto a work surface of an electrode, subjecting the coated electrode to a heat treatment including temperatures in the range of about 700* to 900* C. for a period of time sufficient to eliminate any impurities within said layer, and assembling such heat treated electrodes into a gas impermeable voltage overload arrester structure so that said electrode work surfaces are spaced in facing adjacent relation from each other.
 10. A method as defined in claim 9 wherein the first material is Ba and is present in amounts ranging from about 30 percent to about 90 percent by weight and the second material is Al and is present in amounts ranging from about 10 percent to about 70 percent by weight. 